Because various current consumer electronic devices, such as communication devices, image extraction devices, storage devices, and Internet devices, have been developing the functions of high resolution, high definition, or high storage capacity, it is required to process huge volume of digital data. In order to enable users to transmit considerable quantities of digital data between hosts and electronic devices, most of the consumer electronic devices include popular transmission frameworks of high-speed serial bus, for example, universe serial bus (USB) or IEEE1394 transmission frameworks.
Take the USB transmission framework for example. In the USB2.0, there is a strict standard on the frequencies of the interface communication protocol between hosts and USB devices in low-speed, full-speed, and high-speed conditions for corresponding to different applications. In the low-speed condition, the data rate specification of the data stream of hosts is 1.5 MHz±1.5% and applicable to keyboards and mice. In the full-speed condition, the data rate specification of the data stream of hosts is 12 MHz±0.25% and applicable to audio and microphones. In the high-speed condition, the data rate specification of the data stream of hosts is 480 MHz±0.05% and applicable to video and imaging.
In addition, because multiple data transmission stages are defined in the USB transmission framework, the allowable ranges of receiving frequency by the hosts for receiving data differ. For example, according to the USB transmission framework, three data transmission stages are defined, including a device identification stage, a device configuration stage, and a data transmission stage. The allowable ranges of the receiving frequency by the hosts in each stage for receiving data are not identical. The allowable error of the receiving frequency in the data transmission stage is the smallest. This is because substantial volumes of data are to be transmitted, the range of the receiving frequency must be accurate for preventing erroneous data transmission. Thereby, the frequency sources for USB devices are mostly quartz oscillators, resonance oscillators, or adding digital phase-lock loops (DPLLs) for generating an accurate frequency signal.
FIG. 1 shows an interface data transmission framework of the USB device according to the prior art, which comprises a host 10 and a USB device 12. The host 10 and the USB device 12 are connected to each other via the USB interface therebetween and perform signal transmission. Nonetheless, the requirement in the accuracy of the transmission signal frequency of USB is strict. Thereby, the USB device according to the prior art adopts a quartz oscillator 121 connected to the control chip of the USB device 12 for generating the clock signal and used as the operating frequency of the USB device 12. Nonetheless, using the external quartz oscillator 121 increases the manufacturing cost. Besides, because the clock frequency of the quartz oscillator 121 is fixed, compared with the signal transmitted by the host 10, there is possibility of producing errors.
For solving the problem described above, manufactures integrate the internal resistors and capacitors of the control chip in the USB device for producing an RC oscillator used as the frequency source of the USB device, enabling the frequency source of the USB device to be included inside the control chip thereof. Nonetheless, due to process variations, there are approximately ±25% errors in the frequency of the RC oscillator, which does not comply with the standard for USB drivers.
Accordingly, the present invention provides a transmission interface device capable of calibrating the transmission frequency automatically and the method thereof. When the frequencies of the transmission interface device and the host are compatible, according to the error handling transmitted by the host or the error handling detected by the device from the received data, the transmission device is reset and its frequency is adjusted until the frequency of the transmission device falls within the frequency range.